1. Field of the Invention
The present invention relates to an optical scanner that scans a light flux from a light source to a photosensitive surface of each of a plurality of photoconductors in a main-scanning direction. In particular, the present invention relates to a technique of achieving reduction in space for allocation of an optical system and improvement of an optical characteristic of scan light.
2. Description of the Related Art
Conventionally, in relation to an optical scanning technique that scans a light flux from a light source to a photosensitive surface of each of a plurality of photoconductors in a main-scanning direction, there has been disclosed an image forming device that forms an image such as an electrostatic latent image on the photoconductors by irradiation of a light beam, the image forming device that sets a plurality of reflecting surfaces in a rotational reflector that scans the light beam to the plurality of photoconductors to have an inclination angle different from one another with respect to a rotational axis, and scans the different photoconductor for each of the reflecting surfaces having the inclination angle different from one another (for example, refer to Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2000-2846 and Patent Document 2: Jpn. Pat. Appln. Laid-Open Publication No. 11-218991).
In the conventional art configured as described above, a polygon mirror having the reflecting surfaces each having a reflecting angle different from one another is used, so that both kinds of scanning, that are scanning by and switchover of a light path of a laser beam, can be carried out by a rotational operation of a polygon mirror. Therefore, lowering of cost by reduction in the number of items of parts and by reduction in movable parts, and printing with high precision by simplification of control operation can be achieved.
In the conventional art described above, there also is an invention in which a cylinder lens is arranged in a pre-deflection optical system (refer to Patent Document 1). In this invention, light is considered to be converged in the vicinity of a reflecting surface of the deflecting unit in a sub-scanning direction, and in the post-deflection optical system, the reflecting surface and the image surface of the deflecting unit are considered to have a substantially conjugate relationship in the sub-scanning direction so as to provide a surface tilt correcting function. On the other hand, there is a configuration where the cylinder lens is not included in the pre-deflection optical system. In such a configuration, the post-deflection optical system is considered not to have the surface tilt correcting function (for example, refer to Patent Document 2 and Patent Document 3: Jpn. Pat. Appln. Laid-Open Publication No. 63-273814).
In a conventional optical scanning technique as described above, there is known a configuration where a light source is arranged in each of a plurality of photoconductors each carrying a developer of a color different from one another, and a latent image is formed by the plurality of light sources. However, a configuration such as above requires large space for having an optical system allocated therein and is not desirable in view of space saving and cost reduction.
On the other hand, there is also known a configuration where one LD is used as a light source that forms a latent image on a plurality of photoconductors. In a case of such a configuration, as compared with a configuration where one light source is provided for each of photoconductors as described above, the number of revolutions of a polygon mirror and a drive frequency need to be increased, and obtaining high speed and high precision has been difficult.